A subset of the vanilloid channels (TRPV1-4) are referred to as thermoTRPs to reflect the observation that heat elicits channel opening across a continuum of temperatures with thresholds ranging from 25° C. to 52° C. (Caterina, M. J.; Rosen, T. A.; Tominaga, M.; Brake, A. J.; Julius, D., Nature 1999, 398, 436-441). TRPV3 characteristically responds to innocuous heat >31° C., exhibits exquisite sensitivity around the physiological temperature of humans, 37° C., and sensitizes dramatically following repetitive heating (Smith, G. D.; Gunthorpe, M. J.; Kelsell, R. E.; Hayes, P. D.; Reilly, P.; Facer, P.; Wright, J. E.; Jerman, J. C.; Walhin, J. P.; Ooi, L.; Egerton, J.; Charles, K. J.; Smart, D.; Randall, A. D.; Anand, P.; Davis, J. B., Nature 2002, 418, 186-190; Xu, H.; Ramsey, I. S.; Kotecha, S. A.; Moran, M. M.; Chong, J. A.; Lawson, D.; Ge, P.; Lilly, J.; Silos-Santiago, I.; Xie, Y.; DiStefano, P. S.; Curtis, R.; Clapham, D. E., Nature 2002, 418, 181-186; Peier, A. M.; Reeve, A. J.; Andersson, D. A.; Moqrich, A.; Earley, T. J.; Hergarden, A. C.; Story, G. M.; Colley, S.; Hogenesch, J. B.; McIntyre, P.; Bevan, S.; Patapoutian, A., Science 2002, 296, 2046-2049).
TRPV3 is a nonselective cation channel with permeability for calcium, but also to other cations, for example sodium. Multiple compounds that have been shown to activate TRPV3, include: monoterpenes, camphor (Peier, A. M. et al., 2002; Moqrich, A.; Hwang, S. W.; Earley, T. J.; Petrus, M. J.; Murray, A. N.; Spencer, K. S.; Andahazy, M.; Story, G. M.; Patapoutian, A., Science 2005, 307, 1468-1472; Xu, H.; Blair, N. T.; Clapham, D. E., J Neurosci. 2005, 25, 8924-8937), carvacrol, and thymol (Xu, H.; Delling, M.; Jun, J. C.; Clapham, D. E. Nat. Neurosci. 2006, 9, 628-635; Vogt-Eisele, A. K.; Weber, K.; Sherkheli, M. A.; Vielhaber, G.; Panten, J.; Gisselmann, G.; Hatt, H., Br J Pharmacol. 2007, 151, 530-540; Story, G. M., Mol Cell Neurosci. 2006, 32, 335-343; Vogt-Eisele, A. K. et al., 2007); cinnamaldehyde (Macpherson, L. J. et al., 2006); incensole acetate (Moussaieff, A.; Rimmerman, N.; Bregman, T.; Straiker, A.; Felder, C. C.; Shoham, S.; Kashman, Y.; Huang, S. M.; Lee, H.; Shohami, E.; Mackie, K.; Caterina, M. J.; Walker, J. M.; Fride, E.; Mechoulam, R., FASEB J. 2008, 22, 3024-3034.); and vanilloid analogs, eugenol and ethyl vanillin (Hu, H. Z.; Gu, Q.; Wang, C.; Colton, C. K.; Tang, J.; Kinoshita-Kawada, M.; Lee, L. Y.; Wood, J. D.; Zhu, M. X., J Biol. Chem. 2004, 279, 35741-35748; Vogt-Eisele, A. K. et al., 2007; Xu, H. et al., 2006). Though relatively weak (EC50, ˜40 μM) and nonspecific across TRPs, 2-aminoethoxydiphenylborate (2-APB) and diphenylboronic anhydride (DPBA) have been widely and productively used to characterize key attributes of TRPV3 in cellular assays and electrophysiology (Hu, H. Z. et al., 2004; Chung, M. K.; Lee, H.; Mizuno, A.; Suzuki, M.; Caterina, M. J. J Neurosci. 2004, 24, 5177-5182; Chung, M. K.; Giller, A. D.; Caterina, M. J., J Biol. Chem. 2005, 280, 15928-15941). While heat and direct ligand binding are clearly central to TRPV3 pharmacology, accumulating evidence of potentiation by arachidonic acid, other unsaturated fatty acid derivatives (Hu, H. Z.; Xiao, R.; Wang, C.; Gao, N.; Colton, C. K.; Wood, J. D.; Zhu, M. X., J Cell Physiol. 2006, 208, 201-212), and nitric oxide (Aley, K. O.; McCarter, G.; Levine, J. D., J Neurosci. 1998, 18, 7008-7014; Yoshida, T.; Inoue, R.; Morii, T.; Takahashi, N.; Yamamoto, S.; Hara, Y.; Tominaga, M.; Shimizu, S.; Sato, Y.; Mori, Y., Nat Chem. Biol. 2006, 2, 596-607) suggests that authentic activation involves stimulation of G protein-coupled receptors and downstream second messenger signal cascades (e.g., phospholipase C, protein kinase C) that mediate local inflammatory responses and nociceptor sensitization that could enhance TRPV3 function (Xu, H. et al., 2006) in a pathophysiological, as compared to basal state.
Evidence suggests that transcriptional regulation of the TRPV3 gene restricts its basal expression and is responsible for enhanced expression following nerve injury. Levels of TRPV3 mRNA recovered from rat L4 and L5 DRG neurons is elevated in the spinal nerve ligation model of neuropathic pain, as compared to uninjured rats (U.S. Pat. No. 7,396,910). Similar upregulation of TRPV3 has been observed in sensory neurons following peripheral nerve injury in humans (Facer, P.; Casula, M. A.; Smith, G. D.; Benoham, C. D.; Chessell, I. P.; Bountra, C.; Sinisi, M.; Birch, R.; Anand, P., BMC Neurol. 2007, 7, 11-22; Smith G. D. et al., 2002).
One feature that distinguishes TRPV3 from the other thermoTRPs is its relatively prominent localization in skin (Peier, A. M. et al., 2002; Xu, H. et al., 2002). TRPV3 is also expressed in dorsal root ganglion, trigeminal ganglion, spinal cord and brain (Xu, H. et al., 2002; Smith G. D. et al., 2002). Its distinctive tissue profile, with significant expression in keratinocytes proximal to nociceptive neurons (Chung, M. K.; Lee, H.; Caterina, M. J., J Biol. Chem. 2003, 278, 32037-32046; Chung, M. K.; Lee, H.; Mizuno, A.; Suzuki, M.; Caterina, M. J. J Biol. Chem. 2004, 279, 21569-21575; Peier, A. M. et al., 2002; Xu, H. et al., 2002) as well as upregulation of TRPV3 in disease states is consistent with a likely role of TRPV3 in pain (Caterina M J., Am J Physiol Regul Integr Comp Physiol. 2007, 292, R64-R76; Lee, H.; Caterina, M. J., Pflugers Arch. 2005, 451, 160-167; Güller, A. D.; Lee, H.; Iida, T.; Shimizu, I.; Tominaga, M.; Caterina, M., J Neurosci. 2002, 22, 6408-6414; Chung, M. K. et al., 2003; Chung, M. K.; Lee, H.; Mizuno, A.; Suzuki, M.; Caterina, M. J. J Biol. Chem. 2004, 279, 21569-21575). In a keratinocyte cell line, stimulation of TRPV3 leads to release of inflammatory mediators including interleukin-1. Thus TRPV3 may also play an important role in regulating inflammation, itch (Steinhoff, M. and Biro, T. J. Invest. Dermatology, 2009, 129, 531-535) and pain that results from the release of inflammatory stimuli. In addition, localization of TRPV3 in non-neuronal tissues, especially skin, suggests also that pharmacological modulation of the channel may provide a therapy to treat diseases that impair the skin barrier (Montell, C. Cell, 2010, April 16, 218-220) and have additional, as yet unidentified, benefit for disease states beyond pain. Accordingly, compounds that can modulate one or more functions of TRPV3 can have various therapeutic utilities.